1 Health eResearch Centre, Farr Institute for Health Informatics Research, University of Manchester, Vaughan House, Portsmouth Road, Manchester, M13 9PL, UK. jane.candlish@sheffield.ac.uk.
2 School of Health and Related Research, University of Sheffield, 30 Regent St, Sheffield, S1 4DA, UK. jane.candlish@sheffield.ac.uk.
3 Health eResearch Centre, Farr Institute for Health Informatics Research, University of Manchester, Vaughan House, Portsmouth Road, Manchester, M13 9PL, UK.
4 Utrecht Institute for Pharmaceutical Sciences, Utrecht University, Utrecht, The Netherlands.